1. Technical Field
The present invention relates to an electro-optical apparatus, an electronic apparatus including thin-film transistors on a device substrate, and a method of manufacturing the electro-optical apparatus.
2. Related Art
Among a variety of electro-optical apparatuses, in an active matrix liquid crystal apparatus, for example, liquid crystal is held between a device substrate 10 shown in FIGS. 19a and 19b and a counter substrate (not shown). In the device substrate 10, a pixel-switching thin-film transistor 1c and a pixel electrode 2a electrically connected to a drain of the thin-film transistor 1c is formed in each of a plurality of pixel regions 1e corresponding to intersections between gate lines 3a (scanning lines) and source lines 6a (data lines). The alignment of molecules of the liquid crystal is controlled by an image signal applied to the pixel electrode 2a from the source line 6a through the thin-film transistor 1c in each pixel. A storage capacitor 1h having a portion of a capacitive line 3b which serves as a lower electrode 3c and an extending portion of a drain electrode 6b which serves as an upper electrode 6c is formed in the pixel region 1e and an insulating film 4 for configuring a gate insulating layer 4e of the thin-film transistor 1c is used as a dielectric layer 4c in the storage capacitor 1h (FIG. 3 of Japanese Patent No. 2584290)
Meanwhile, even in an electro-optical apparatus using the bottom-gate thin-film transistor 1c shown in FIGS. 19a and 19b, as shown in the left side of FIG. 19b and FIG. 19c, when thin-film transistors 1g and 1g′ used in a gate line driving circuit or a source line driving circuit are formed using a method of manufacturing the thin-film transistor 1c, a driving IC having the gate line driving circuit or the source line driving circuit included therein does not need to be separately used. That is, when the gate line 3a, the gate insulating layer 4e and an active layer 7a are formed and at the same time a signal line 3g for configuring a gate electrode of the thin-film transistor 1g, the gate insulating layer 4g and an active layer 7g are formed, a driving circuit may be included in the device substrate 10 with a smaller number of processes. In the driving circuit, a gate wiring 3g′ and a drain wiring 6g need to be electrically connected and, in this case, a conductive pattern 2s is electrically connected to a lower conductive layer 3s extending from the gate wiring 3g′ and an upper conductive layer 6s extending from the drain wiring 6g through contact holes 82 and 89 formed in the insulating film 4 or a passivation film 8.
However, when the active layer 7g of the thin-film transistor 1g used in the driving circuit is formed using an amorphous silicon film similar to the active layer 7a of the thin-film transistor 1c, ON current is too low compared with a case of using a polysilicon film and thus a high-speed operation in the gate line driving circuit or the source line driving circuit cannot be realized. In particular, in the thin-film transistor 1c for switching the pixel, when the thickness of the insulating film 4 used in the gate insulating layer 4e is increased for the purpose of reducing parasitic capacitance, the thickness of the gate insulating layer 4e of the thin-film transistor 1g is also increased. Thus, the ON current of the thin-film transistor 1g is too low to be used in the driving circuit.